Solarization-stable ultraviolet filter glasses for the 280-500 nm transmission range

ABSTRACT

Alkali silicate glasses, colorized with Co 2+  or with Co 2+  and Ni 2+ , and having the composition: 
     
         ______________________________________                                    
 
    
     SiO 2          52-71% by weight                                        
PbO               2.9-16.8% by weight                                     
SnO 2          0.1-1.65% by weight                                     
Na 2  O        6.7-16.7% by weight                                     
K 2  O         0.5-9.9% by weight                                      
Na 2  O + K 2  O                                                    
                  13.3-18.3% by weight                                    
[NiO + CoO        0.1-4.4% by weight                                      
Ni 2  O 3  + Co 2  O 3  ]                                     
As 2  O 3  + Sb 2  O 3                                        
                  0.05-0.5% by weight                                     
Σ RO        0-8.6% by weight                                        
B 2  O 3    0-8.5% by weight                                        
Al 2  O 3   0-0.55% by weight                                       
ZnO               0-10.5% by weight,                                      
______________________________________                                    
 
     in which R is Mg, Ca, Sr, Ba or a combination thereof, are disclosed. The composition of the present invention is not to include CeO 2 . The alkali silicate glasses of the invention are useful as optical filter glasses.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.179,063, filed Apr. 8, 1988, now U.S. Pat. No. 4,906,597, which, inturn, is a division of application Ser. No. 136,191, filed Dec. 21,1987, now U.S. Pat. No. 4,820,326.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates, generally, to alkali silicate glasseswhich are used as the basic glasses for the manufacture of selectivefilter glasses. More particularly, the present invention relates to themanufacture of selective filter glasses, colored with Co²⁺ or with Co²⁺and Ni²⁺, which have transmission ranges primarily in the ultravioletand visible spectral region between 280 and 500 nanometers (nm). Theseion-colored glasses are imbued with the characteristic absorption bandsof Co²⁺ and Co²⁺ together with Ni²⁺ and, therefore, depending upon thelayer thickness, produce selective bell-shaped transmission bands, eachsurrounded by two stop ranges.

The most important characteristics of these so-called band pass filters,when the layer thickness is known, are the maximum of spectraltransmission in the transmission band of τ_(max) and thehalf-wavelengths λ'1/2 and λ"1/2 with a spectral transmission of τ_(max)/2. The mid-point between the half-wavelengths λ'1/2 and λ"1/2 is calledthe mean wavelength λ_(m) ; the distance from λ'1/2 to λ"1/2 is known asthe half-value width (HW). (See, FIG. 1.)

In research, engineering and medicine, these glasses are used, forexample, as conversion filters in a narrow spectral region and, moreparticularly, are used in the filtering of UV light sources in theemission range from 200 to 1100 nm, with particular significance as passfilters in the ultraviolet spectral region from 250 to 400 nm and asstop filters in the spectral region of approximately 420 to 680 nm. Theglasses can readily have compositions that assure high chemicalresistance to acids, alkalis and water.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1:

FIG. 1 shows the most important characteristics of these so-called bandpass filters.

FIG. 2:

FIG. 2 shows emission lines of the Sylvania Germicidal Emitter, G15 T8.

FIGS. 3 and 4:

In FIGS. 3 and 4, transmission curves are plotted, from 200 to 850 nmfor both before and after solarization testing. The curves demonstratethe very severe change in filter properties in the transmission bandfrom 260 to 520 nm.

FIG. 5:

FIG. 5 shows the absorption relationship of filtered high-energy UVcomponents.

FIG. 6:

FIG. 6 shows glasses capable of being used for the present invention interms of the width of their transmission bands.

FIG. 7:

FIG. 7 shows the steepness of the absorption edge of glass containingSnO₂.

FIG. 8:

FIG. 8 shows a comparison of the transmission curves of a conventionalglass (BG 3) with the glass of Example 1.

DESCRIPTION OF THE PRIOR ART

Alkali silicate glasses colored with Co²⁺ or with Co²⁺ and Ni²⁺ areavailable from the major manufacturers of optical filter glass and,therefore, known to the art, e.g. U.S. Pat. No. 3,902,881. Examplesinclude BG 3, FG 3, UG 1 (Schott catalogue), 1-61, 7-51 (Corningcatalogue), BD 37-93 (VEB Jena catalogue) and others. A drawbackexperienced with these glasses is that if they are exposed toultraviolet radiation for a relatively long duration, the spectraltransmission of these glasses can change, predominantly in theultraviolet spectral range. The absorption increases up to a certainsaturation value. This undesirable phenomenon is called solarization.The aforementioned saturation value is attained at varying degrees ofquickness, depending upon the duration and intensity of the irradiationand on the distance of the filter glass from the light source. The glass"ages" and then on it is only conditionally usable for its intendedpurpose.

For ascertaining the solarization properties of filter glasses, thefollowing testing procedure is typical and generally applicable:

    ______________________________________                                        thickness of sample:                                                                            1 mm                                                        light source:     low-pressure mercury lamp                                                     (maximum emission at 254                                                      nm), type: "Sylvania                                                          Germicidae," G 15 T 8,                                                        sold by Philips (emission                                                     spectrum, see FIG. 2)                                       filtering of source:                                                                            none                                                        exposure time:    75 hours                                                    sample-to-source distance:                                                                      140 mm                                                      measured variable Δτ (transmission before                                             and after UV exposure)                                      ______________________________________                                    

In FIGS. 3 and 4, transmission curves are plotted, from 200 to 850 nmfor both before and after the above-described solarization testingprocedure, taking a commercially available blue alkali silicate glass asan example (BG 3 made by Schott Glaswerke, Mainz, Federal Republic ofGermany). The curves demonstrate the very severe change in filterproperties in the transmission band from 260 to 520 nm.

The prior art further includes high absorbent lead-containing glasses,as disclosed by U.S. Pat. No. 4,520,115. These glasses, however, containCeO₂, which would strongly stain the glasses of the present inventionand thereby render the glasses of the invention unsuitable for theirintended purposes as, for example, described above.

DESCRIPTION OF THE INVENTION

An object of the present invention is to provide UV filters, made ofalkali silicate glasses, having a high chemical stability to acids,alkalis and water and having a high solarization resistance when exposedto ultraviolet light for relatively long periods of time.

The foregoing and related objects are accomplished by the use of analkali silicate glass, colored with Co²⁺ or with Co²⁺ and Ni²⁺, as anoptical filter glass, which has the following composition:

    ______________________________________                                        SiO.sub.2            52-71% by weight                                         PbO                  2.9-16.8% by weight                                      SnO.sub.2            0.1-1.65% by weight                                      Na.sub.2 O           6.7-16.7% by weight                                      K.sub.2 O            0.5-9.9% by weight                                       Na.sub.2 O + K.sub.2 O                                                                             13.3-18.3% by weight                                     NiO + CoO            0.1-4.4% by weight                                       As.sub.2 O.sub.3 + Sb.sub.2 O.sub.3                                                                0.05-0.5% by weight                                      Σ(MgO + CaO + SrO + BaO)                                                                     0-8.6% by weight                                         B.sub.2 O.sub.3      0-8.5% by weight                                         Al.sub.2 O.sub.3     0-0.55% by weight                                        ZnO                  0-10.5% by weight.                                       ______________________________________                                    

The glasses of the claimed invention are not to include CeO₂.

It has surprisingly been discovered that in the present invention, theUV components that bring about the solarization are already absorbed inthe surface layers of the filters and no further solarization can bebrought about in the filter itself. A comparable effect can be attainedby filtering the UV light source with 1-mm-edge filters for 280, 295,305 and 320 nm. By this means, the highest-energy UV components areabsorbed and are, accordingly, no longer available as excitation energyfor forming pigment centers, which are also the cause for solarizationin the glasses. This relationship is described in FIG. 5. By doping theglasses with PbO, SnO₂ and/or TiO₂, Fe₂ O₃ and V₂ O₅, the absorptionedge of the basic alkali silicate glasses can be shifted up to 60 nmtoward the longer-wave spectral region.

Glasses capable of being used for the present invention, which have alayer thickness of 1 mm, can be divided among the following groups interms of the width of their transmission bands (see, FIG. 6):

                  TABLE 1                                                         ______________________________________                                        τ max.sup.(%)                                                             exposure                                                                      be-             λ'1/2                                                                          λ"1/2                                                                        λm                                                                          HW                                         fore    after.sup.+                                                                           (nm)*   (nm)  (nm) (nm) Colorant                              ______________________________________                                        I.   88     87      290   460   375  170  Co.sup.2+                           II.  89     87      300   490   395  190  Co.sup.2+                           III. 82     81      310   390   350   80  Co.sup.2+  + Ni.sup.2+              ______________________________________                                         .sup.+ Exposure conditions as in aforesaid test procedure.                    *values ± 5 nm.                                                       

In contrast to the filters of the present invention, Table 2 presentscomparative test results with equivalent commercially available bandpass filters and conversion filters:

                  TABLE 2                                                         ______________________________________                                        τ max.sup.(%)                                                             exposure                                                                      be-              λ'1/2                                                                          λ"1/2                                                                       λm                                                                          HW                                         fore     after.sup.+                                                                           (nm)*   (nm) (nm) (nm) Colorant                              ______________________________________                                        BG3.sup.1                                                                           88     13      275   450  362  175  Co.sup.2+                           FG3.sup.2                                                                           89     42      270   550  410  280  Co.sup.2+                           UG1.sup.3                                                                           78     71      310   390  350   80  Co.sup.2+  + Ni.sup.2+              ______________________________________                                         .sup.+ Exposure conditions as in aforesaid test procedure.                    *values ± 5 nm                                                             .sup.1 BG = blue, bluegreen and band filters; band pass filters               .sup.2 FG = blue and brown color filters; conversion filters                  .sup.3 UG = black and blue glass band pass filters                       

(1) BG=blue, blue-green and band filters; band pass filters

(2) FG=blue and brown color filters; conversion filters

(3) UG=black and blue glass band filters.

The shift of the UV absorption edge in groups I and II toward longerwavelengths is apparent. To some extent, this narrows the transmissionband in the farther UV band (260 to 310 nm).

According to the invention, because of the PbO and SnO₂ content in thevarious quantity ranges claimed for synthesizing the alkali silicateglasses, not only is a shift of the absorption edge to the longer-wavespectral region achieved, but also a marked reduction is brought aboutin the tendency toward solarization of the glasses.

The steepness of the absorption edge is favorably affected, during onthe type of glass, by SnO₂ in the range of from 0.1 to 1.7% by weight,i.e., by means of SnO₂, a greater steepness of the absorption edge isattained (see, FIG. 7). As a result, the midpoint of the transmissionband of the filters, which is measurable by the variable λ_(m) (nm), ischanged only negligibly as compared with the conventional filters havinga greater tendency toward solarization (compare, Table 1 and 2).

The modification of the alkali silicate synthesis by PbO and SnO₂necessitates particular provisions in the production of bubble-free,homogeneous optical filter glasses. To this end, according to thepresent invention, in addition to the classical refining agents As₂ O₃and/or Sb₂ O₃, depending on the basic glass synthesis, F, Cl, NH₄ Cl andSO₃ are used, above all, for reinforcing the refining action. Inaddition to from 0-0.5% by weight of F⁻, the glasses used may alsocontain from 0-3% by weight of Li₂ O to lower the temperature for theviscosity range between 10² and 10⁶ dPa·s.

The shift of the absorption edge is not only attainable by means of PbOand SnO₂, but also by means of the ions having absorption bands between250 and 400 nm, especially by means of the ions Ce⁴⁺, Ti⁴⁺, Fe³⁺, V⁵⁺,and Pd²⁺. Together with the refining agents, As₂ O₃ and/or Sb₂ O₃, andthe coloring "filter ions," Co²⁺ and Ni²⁺, the concentration of theseions should be no more than at a minimal level. This is because theinteraction of two ambivalent ions in irradiation with ultraviolet lightleads to quite pronounced solarization effects in alkali silicateglasses. This relationship is known and has been described in variouspublications, including:

Hideo Hosono et. al., J. of NCS 63 (1984), pages 357-363; and

Klaus Bermuth et. al., Glastechn. Ber. [Reports in Glass Technology] 58(1985) 3, pages 52-58.

From Tables 1 and 2, it becomes clear from the example of group II ofthe glasses having the composition according to the invention, that thelocation of the absorption edge at 310 nm is not affected by the PbO andSnO₂ components, but, instead, that a considerable reduction insolarization occurs as compared with glasses in which PbO and SnO₂ areabsent. It is conceivable that by the incorporation of Pb²⁺ and Sn²⁺ orSn⁴⁺, a structural change in the silicate glasses takes place, such thatthe formation of pigment centers, due to UV irradiation, is renderedmore difficult, or is even suppressed entirely.

The transmission of the basic glasses is characterized by the specificabsorption of at least one of the following components:

1-1.5% by weight of CoO (optionally in the form of CoO and Co₂ O₃); and

0-4.4% by weight of NiO (optionally in the form of NiO and Ni₂ O₃).

In Table 3, which follows on the next page, some examples from theuseful composition range are provided:

                  TABLE 3                                                         ______________________________________                                        Examples of Compositions (%) by weight                                        Group I        Group II     Group III                                         1          2       3        4     5     6                                     ______________________________________                                        SiO.sub.2                                                                            64.00   57.30   65.20  70.50 54.60 52.15                               B.sub.2 O.sub.3                                                                      8.65    8.45    17.30  --    4.00  5.00                                Al.sub.2 O.sub.3                                                                     --      --      3.00   --    0.30  0.55                                Li.sub.2 O                                                                           --      --      --     3.00  --    --                                  Na.sub.2 O                                                                           8.60    6.70    8.10   16.70 8.40  11.40                               K.sub.2 O                                                                            8.30    6.60    1.50   0.50  9.90  5.65                                MgO    --      1.60    --     --    --    1.30                                CaO    --      1.50    --     1.85  --    4.80                                SrO    --      1.55    --     1.90  --    --                                  BaO    1.90    --      --     0.45  --    2.50                                ZnO    1.10    10.50   --     --    1.80  5.70                                PbO    4.95    4.00    3.40   2.90  16.75 2.90                                TiO.sub.2                                                                            --      --      --     0.80  --    --                                  SnO.sub.2                                                                            1.20    1.25    0.60   0.30  0.10  1.65                                As.sub.2 O.sub.3                                                                     0.25    0.10    0.50   0.10  0.05  0.05                                Sb.sub.2 O.sub.3                                                                     --      0.10    --     --    0.25  --                                  NH.sub.4 Cl                                                                          0.15    --      --     0.30  --    --                                  Cl     --      --      0.05   --    --    --                                  F      --      --      0.10   0.50  0.10  --                                  SO.sub.3                                                                             0.10    --      0.10   --    0.20  0.10                                CeO.sub.2                                                                            --      --      --     --    0.15  0.25                                Fe.sub.2 O.sub.3                                                                     --      --      0.05   --    --    0.15                                V.sub.2 O.sub.5                                                                      --      0.05    --     --    0.10  --                                  Co     0.20    0.30    --     --    0.75  --                                  CoO    0.60    --      0.10   0.20  --    1.50                                Ni     --      --      --     --    2.55  --                                  NiO    --      --      --     --    --    4.35                                Totals 100.0   100.0   100.0  100.0 100.0 100.0                               ______________________________________                                    

Finally, FIG. 8 shows a comparison of the transmission curves of aconventional glass (BG 3) with the glass of Example 1, in each case,before and after exposure. In the glass of Example 1, the transmissioncurves of the glass before and after the exposure are identical, i.e.,the exposure does not cause any loss in transmission.

With respect to the test conditions for the exposure, once again thoseof the aforesaid test procedure were selected.

EXEMPLARY EMBODIMENT

The invention will now be further described with reference being made toan exemplary embodiment thereof. It should, however, be recognized thatthe following example is not intended as a definition of the scope orlimitations of the present invention.

As illustrative of the present invention, for producing 100 kg of Co²⁺-colored alkali silicate glass having the composition of Example 1, thefollowing ingredients are mixed into a uniform mass of raw material in amixing drum:

64.064 kg of Sipur (SiO₂)--"Sipur" is a trademark for silicon dioxide ofthe Bremthaler Quarzitwerke, Usingen, Federal Republic of Germany.

15.367 kg of boric acid (H₃ BO₃)

23.181 kg of sodium hydrogen carbonate (NaHCO₃)

12.205 kg of potassium carbonate (K₂ CO₃)

2.480 kg of barium carbonate (BaCO₃)

1.101 kg of zinc oxide (ZnO)

5.067 kg of lead oxide red (Pb₃ O₄)

1.200 kg of stannic oxide (SnO₂)

0.253 kg of arsenic oxide (As₂ O₃)

0.150 kg of ammonium chloride (NH₄ Cl)

0.230 kg of sodium sulfate (Na₂ SO₄)

0.200 kg of cobalt metal powder (Co)

0.844 kg of cobalt oxide (Co₂ O₃)

This mixture is melted down in batches over a period of 6 to 7 hours at1280° to 1320° C. in ceramic or platinum fusing equipment. The degassingof the fused mass takes place in the temperature range of from 1470° to1500° C. over a period of from 2 to 4 hours.

The homogenization of the fused mass is performed at 1250° to 1480° C.The time required for this is approximately 2 to 3 hours. The resultingfused glass is then poured into a pre-heated mold.

While only several embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art that manymodification may be made thereunto without departing from the spirit andscope of the invention.

What is claimed is:
 1. An alkali silicate solarization-stable ultraviolet glass, transmitting in the 280-500 nm range, for use as an optical filter glass, said alkali silicate glass being colored with a member selected from the group consisting of Co²⁺ and (Co²⁺ and Ni²⁺), comprising:

    ______________________________________                                         SiO.sub.2         52-71% by weight                                             PbO               2.9-16.8% by weight                                          SnO.sub.2         0.1-1.65% by weight                                          Na.sub.2 O        6.7-16.7% by weight                                          K.sub.2 O         0.5-9.9% by weight                                           Na.sub.2 O + K.sub.2 O                                                                           13.3-18.3% by weight                                         NiO + CoO         0.1-4.4% by weight                                           As.sub.2 O.sub.3 + Sb.sub.2 O.sub.3                                                              0.05-0.5% by weight                                          Σ RO        0-8.6% by weight                                             B.sub.2 O.sub.3   0-8.5% by weight                                             Al.sub.2 O.sub.3  0-0.55% by weight                                            ZnO               0-10.5% by weight                                            ______________________________________                                    

wherein, R is an element selected from the group consisting of Mg, Ca, Sr, Ba and a combination thereof,said alkali silicate solarization-stable ultraviolet glass not including CeO₄ as a component thereof.
 2. An alkali silicate solarization-stable ultraviolet glass, transmitting in the 280-500 nm range, for use as an optical filter glass, said alkali silicate glass being colored with a member selected from the group consisting of Co²⁺ and (Co²⁺ and Ni²⁺), comprising:

    ______________________________________                                         SiO.sub.2         52-71% by weight                                             PbO               2.9-16.8% by weight                                          SnO.sub.2         0.1-1.65% by weight                                          Na.sub.2 O        6.7-16.7% by weight                                          K.sub.2 O         0.5-9.9% by weight                                           Na.sub.2 O + K.sub.2 O                                                                           13.3-18.3% by weight                                         [NiO + CoO +      0.1-4.4% by weight                                           Ni.sub.2 O.sub.3 + Co.sub.2 O.sub.3 ]                                          As.sub.2 O.sub.3 + Sb.sub.2 O.sub.3                                                              0.05-0.5% by weight                                          Σ RO        0-8.6% by weight                                             B.sub.2 O.sub.3   0-8.5% by weight                                             Al.sub.2 O.sub.3  0-0.55% by weight                                            ZnO               0-10.5% by weight                                            ______________________________________                                    

wherein, R is an element selected from the group consisting of Mg, Ca, Sr, Ba and a combination thereof,said alkali silicate solarization-stable ultraviolet glass not including CeO₂ as a component thereof. 